Trouble defining markup functiion

[Carl Sorensen]

I'm trying to define a markup function for establishing a common set of 
formatting for a number of text markups.

%%% beginning of sample code

\version "2.19.82"

\displayScheme
\markup{\sans{\fontsize #10 "C"}}  % Just used to show the scheme markup 
command -- this is what I'm trying

#(define-markup-command  (chord-name-markup layout props chord-name) (markup?)
   "Display a chord name in the desired formatting"
   (interpret-markup layout props 
     (make-line-markup (#:sans (#:fontsize 10 chord-name)))))


\markup \chord-name-markup "E"

%%% end of code

I've used displayScheme to get the representation of the markup function.  I've 
found that is uses #:line so that I have to use make-line-markup.  

When I run this code, I get

Processing 
`/var/folders/q5/88k2s1717qv1v7rq4tqz53k80000gn/T/frescobaldi-fmnvoopw/tmpc0ltmn4y/document.ly'
Parsing.../var/folders/q5/88k2s1717qv1v7rq4tqz53k80000gn/T/frescobaldi-fmnvoopw/tmpc0ltmn4y/document.ly:9:32:
 In expression (#:fontsize 10 chord-name):
/var/folders/q5/88k2s1717qv1v7rq4tqz53k80000gn/T/frescobaldi-fmnvoopw/tmpc0ltmn4y/document.ly:9:32:
 Wrong type to apply: #:fontsize

Apparently, in the context of make-line-markup I can't use #:fontsize as the 
first element in a list, because it's not applyable.

How can I do this properly?

Thanks,

Carl